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Economic and Environmental Benefits of Biodiversity David Pimentel; Christa Wilson; Christine McCullum; Rachel Huang; Paulette Dwen; Jessica Flack; Quynh Tran; Tamara Saltman; Barbara Cliff BioScience, Vol. 47, No. 11. (Dec., 1997), pp. 747-757. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199712%2947%3A11%3C747%3AEAEBOB%3E2.0.CO%3B2-H BioScience is currently published by American Institute of Biological Sciences.

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Economic and Environmental

Benefits of Biodiversity

The annual economic and environmental benefits of biodiversity in the United States total approximately $300 billion David Pimentel, Christa Wilson, Christine McCullum, Rachel Huang, Paulette Dwen,

Jessica Flack, Quynh Tran, Tamara Saltman, and Barbara Cliff

A

11 ecosystems and human societies depend on a healthy and tlroductive natural environment that contains diverse plant and animal species. The earth's biota is comtlosed of an estimated 1 0 million species of plants, animals, and microbes (Pimm et al. 1995). In the United States, there are an estimated 750.000 stlecies. of which small organisms, such as arthropods and microbes, make up 95%.' Although approximately 6 0 % of the world's food supply comes from rice, wheat, and corn (Wilson 1988), as many as 20,000 other plant species have been used by humans as food. Some vlants and akimals provide human; with essential medicines and other diverse, useful ~ r o d u c t s For . instance. some plants i n d microbes help to d&rade chemical pollutants and organic wastes and recycle nutrients throughout the ecosystem. The rapidiy growing world population and increased human activity threaten many of these species. The current extinction rate of species ranges from approximately 1000 to 10,000 times higher than natural extinction rates (Kellert and Wilson

Some aspects of

conserving biodiversity

are expensive, although

they may return

major dividends

1993), and if this trend continues, as many as 2 million species of plants and animals will be exterminated worldwide by the middle of the next century (Pimm et al. 1995). This forecast is alarming because biodiversity is essential for the sustainable functioning of the agricultural, forest, and natural ecosystems on which humans depend (Myers 1994, Raven and Johnson 1992, Wilson 1994).For example, the loss of a key species (e.g., a pollinator) can cause the collapse of an ecosystem (Heywood 1995). When humans cause extinctions or pollute or deplete resources on which biological services are based, contributions from biodiversity are jeopardized. For example, although the United States spends $150 billion each year to clean polluted waDavid Pimentel (e-mail: dpl8@cornell. ter, air, and soil (Allen 1996), 4 0 % edu) is a professor in the College of of the lakes in the United States are Agriculture and Life Sciences at Cornell unfit for swimming and other uses University, Ithaca, NY 14853-0901. (Zimmer 1996). This pollution not Christa Wilson, Christine McCullum, only threatens public health, but also Rachel Huang, Paulette Dwen, Jessica reduces aquatic biodiversity. Flack, Quynh Tran, Tamara Saltman, In this article, we analyze the vital and Barbara Cliff are graduate students services that are provided by all biota in the College of Agiculture and Life Sciences at Cornell University, Ithaca, NY 14853-0901. 0 1997 American Institute of Biological Sciences.

Decembev 1997

'P. H. Raven, 1996, personal communication. Missouri Botanical Garden, St. Louis, MO.

(biodiversity), including their genes and biomass, to humans and to the environment. We assess the economic and environmental benefits of the following major contributions of biodiversity: organic waste disposal, soil formation, biological nitrogen fixation, crop and livestock genetics, biological pest control, plant pollination, and pharmaceuticals. Such an assessment can serve as a foundation t o develop strategies and policies t o preserve biological diversity and maintain ecosystem integrity.

Biomass and the recycling of organic wastes Humans, other animals, and microbes depend on plants to collect solar energy and to produce and store essential biomass and nutrients. Including managed agricultural and forestry biomass production, more than 50% of total photosynthetic production on land is used by human^.^ T o produce enough animal food products for the growing world population, approximately 20 billion domestic animals are maintained worldwide, 9 billion of which are raised in the United States (Table 1; Agrostat 1992, USBC 1995, USDA 1995).The biomass of domestic animals in the United States totals 4.5 times that of the human population. Worldwide, domestic animals outweigh the human population by 2.5 times (Table 1).Nearly one-third of the world's ID. Pimentel, C. Wilson, C. McCullum, R. Huang, P. Dwen, J. Flack, Q. Tran,T. Saltman, B. Cliff, unpublished manuscript.

74 7

Table 1. T o t a l n u m b e r a n d biomass of humans, domestic animals, crops, a n d wastes.

soil or Droducts that are " grown in soil for their survival. More than Group Number Biomass (wet) Wastes (wet)" 9 9 % of the total worldwide human ( X 109) ( X lo9 kg) ( X lo9 t ) food supply is produced on land, Humans whereas only 0 . 6 % comes from United States 0.26b 18.4a 0.26 oceans and other aquatic ecosystems World 6' 420' 6 ( F A 0 1991). Domestic animals Diverse soil biota facilitate soil United States 9d 90a 1.1

World 2 0' 1000' 14

formation and improve it for crop Crops production. One square meter of soil United States 3000' 1.7 frequently supports populations of World 30,000' 15 approximately 200,000 arthropods 38.06 Total and enchytraeids and billions of mi"Estimated based on the average weight of a human and average weight of a domestic animal.

crobes (Pimentel et al. 1995). One bUSBC 1994

hectare of high-quality soil contains 'PRB 1995

dUSDA 1993 (Two-thirds poultry)

an average of 1300 kg of earthworms, eAgrostat 1992 (Two-thirds poultry)

1000 kg of arthropods, 3000 kg of 'Estimated based on the average weight of crops per hectare and the number of hectares in

bacteria, 4000 kg of fungi, and many production in the United States and the world.

other plants and animals (Pimentel land area and one-half of US land is are recycled by decomposers, the con- et al. 1992). Earthworms bring between 1 0 and used to grow wild and cultivated plants tribution made by decomposer or500 t ha-'. yr-' of soil to the surface that are fed to domestic animals. ganisms is worth more than $62 bilEach year, humans, livestock, and lion per year in theunited States (where (Pimentel et al. 1995), whereas incrops produce approximately 38 bil- 3.1 billion tons of organic waste is sects often bring between 1 and lion metric tons of organic wastes recycled) and more than $760 billion 1 0 t ha-' . yr-I of soil t o the surface worldwide. These wastes are recycled per year worldwide (Table 2 and Fig- (Pimentel et al. 1995). Earthworms by a variety of decomposer organ- ure 1).This calculation does not take may ingest as much as 500 t ha-' . isms (Table 1).We estimate the eco- into account the benefits of decreased yr-' of soil, thereby churning and nomic benefit of these waste dis- environmental pollution, the recy- mixing the soil (Pimentel et al. 1995). posal activities to be $0.02/kg, based cling of nutrients. the decrease in the Similarly, organisms like the desert on the information that it costs nee2 for landfills,' and the significant snail Tvochoidea seetzenii help to form approximately 1000 kg ha-I . $0.04-0.044lkg to collect and dis- reduction in human diseases. yr-' of soil, an amount that is equivapose of organic wastes that are produced in the Village of Cayuga Biodiversity and soil formation lent to the annual rate of soil formation by wind-borne dust deposits Heights, New York, or in the city of Madison, Wisconsin (Einstein 1995). Fertile soil is a n essential component (Shachak et al. 1995). These comAssuming a conservative value of of the world's ecosystems because all bined activities of snails, earthworms, $0.02/kg for all organic wastes that plant and animal species need either and other organisms redistribute nutrients, aerate the soil, facilitate topTable 2. T o t a l estimated e c o n o m i c benefits of biodiversity i n t h e United States a n d soil formation, and increase rates of water infiltration, thereby enhancw o r l d w i d e (see t e x t f o r details). ing plant productivity (Pimentel et Activity World (x $109) United States (x $ l o 9 ) al. 1995). Despite the activities of soil biota Waste disposal and the mechanical mixing of soil by Soil formation Nitrogen fixation agricultural machinery, soil formaBioremediation of chemicals tion on cropland is slow. It is even Crop breeding (genetics) slower under natural forest and grassLivestock breeding (genetics) land conditions. For example, under Biotechnology agricultural conditions it takes apBiocontrol of pests (crops) Biocontrol of pests (forests) proximately 500 years t o form 2 5 Host plant resistance (crops) mm of soil, whereas under forest Host plant resistance (forests) conditions it takes approximately Perennial grains (potential) 1000 years t o form the same amount Pollination Fishing of soil (Pimentel et al. 1995). Hunting Because earthworms and other Seafood invertebrate species bring between Other wild foods 1 0 and 500 t . ha-' . yr-l of subsurface Wood products soil to the surface, we estimate that Ecotourism Pharmaceuticals from plants the presence of soil biota aids the Forests sequestering of carbon dioxide formation of approximately 1t .ha-' . Total yr-' of topsoil (Pimentel et al. 1995). 74 8

BioScience Vol. 47 No. 11

Using this assumption, and a value to agriculture of approximately $12 per ton of topsoil (Pimentel et al. 1995), a conservative total value of soil biota activity to soil formation on US agricultural land (approximately 400 million hectares) is approximately $5 billion per year (Table 2). For the 4.5 billion hectares of world agricultural land, soil biota contribute approximately $25 billion per year in topsoil value (Table 2).

Other 9.70% Carbon dioxide ucq Waste rec)cllng

Ecolounum

17.08%

3.07% Sitrnpen I atio ion

Nitrogen fixation Nitrogen is essential for plant growth, and an insufficient quantity of it frequently limits biomass production in both natural and agricultural ecosystems. More than 77 million tons of commercial nitrogen is used in world agriculture each year, at a cost of approximately $38.5 billion (USDA 1995). Soil nitrogen is increased not only by commercial fertilizers but also by the addition of animal wastes and the retention of crop residues. However, some of the best sources of nitrogen for crop and other plants are nitrogen-fixing plants and obligate endophytic diazotroph bacteria (Dobereiner 1995). Biological nitrogen fixation is a process in which atmospheric N, is converted into substrates of nitiogen that plants can use (Dobereiner et al. 1995).Biological nitrogen fixation in the United States yields approximately 14 x l o 6 tlyr of usable nitrogen, with a value of $8 billion (Table 2; Bezdicek and Kennedy 1988).This fixed nitrogen is equal to approximately half of the commercial nitrogen fertilizer applied to US farmland every year (USBC 1995). Worldwide, 140-170 x l o 6 tlyr of nitrogen, valued at approximately $90 billion, is fixed by many microorganisms in both agricultural and natural ecosystems (Table 2 and Figure 1; Bezdicek and Kennedy 1988, Peoples and Craswell 1992). Nitrogen fixation in leguminous plants is dominated by a variety of endosymbiotic bacteria. This process fixes an average of 80 k g . ha-I . yr-' of nitrogen worldwide. In addition, recent discoveries indicate that obligate endophytic diazotroph bacteria add as much as 150 kg . ha-I . yr-' of nitrogen to agricultural and natural ecosystems (Dobereiner 1995). December 1997

3%

Biorernediation

Seafood and other wlld f Crop and l~\estockbreed~ng

Pollination

6.83%

-? R- I M-

3.1196

Pcrcn,,,al c,opa

H a t plant reslstanie

Figure 1. The proportion of economic benefits to world society from biodiversity.

Biological nitrogen fixation is the major alternative to the use of commercial nitrogen fertilizer in agriculture (Dobereiner and Pedrosa 1987). In the United States and other developed countries, approximately 30% of the fossil energy used in agriculture is associated with the vroduction of nitrogen fertilizer (Pimentel 1980). As natural gas, coal, and oil supplies become increasingly scarce and more expensive, contributions from biological nitrogen fixation will become even more vital to the productivity of future agricultural systems.

Bioremediation of chemical pollution

resulted in an estimated 400,000600,000 hazardous waste sites just in the United States (Yount and Williams 1996) and countless more throughout the world. Chemicals that are toxic to the environment or to humans must be removed. Removing chemicals from the environment (remediation) can be achieved by bidlogical, physical, chemical, and thermal methods. Biological treatments, which use microbes and plants to degrade chemical materials, can both decontaminate polluted sites (bioremediation) and purify hazardous wastes in water (biotreatment). Overall, biological methods are more effective than physical, chemical, and thermal methods, because the latter methods often simply transfer the pollutant to a different medium instead of con-

verting it to a less toxic substance, as

biological methods often do. In ad-

dition, incineration of many chemi-

cals produces dioxins, which are

highly carcinogenic. Currently, ap-

proximately 75% (by weight) of the

chemicals released into the environ-

ment can be degraded by biological

organisms3 and are potential targets

of both bioremediation and biotreat-

ment. The ability of bioremediation

to provide continuous cleanup of

contaminated sites, such as agricul-

Advances in technology have resulted in the production of a wide range of chemicals, many of which have contributed to ecosystem pollution. Currently, some 70,000 different chemicals are used in the United States and released into the environment through soil, water, and air (Newton and Dillingham 1994); an estimated 100,000 chemicals are used worldwide (Nash 1993). Nearly 10% of the chemicals used in the United States are known carcinogens (Darnay 1994).In the United States, yearly chemical releases total over 290 billion kg (Montague 1989), or more than 1100 kg per person per year.

Over the years, the accumulation of 3M.Carroquino, 1995, personal communica-

chemicals in the environment has tion. Cornell University, Ithaca, NY.

749

tural ecosystems with toxic pesticide residues, is a significant advantage of this method. Furthermore, a significant degree of self-regulation is present in such biological systems because the added microbes survive by consuming and degrading chemicals but die when the nutrient sourcethat is, the pollutant-is reduced or eliminated. Most chemicals are released primarily into the air and into water (Alexander 1994), but some chemicals are also released into the soil. Approximately 23 % of all terrestrial ecosystems have been exposed to toxic chemicals (Tadesse et al. 1994). Nearly 80% of bioremediation efforts of the US Environmental Protection Agency now focus o n eliminating soil pollution because most pollutants end up in soil and many organisms are present in the soil (EPA 1994a).Anderson (1978)reports that a favorable temperate forest soil may support up t o 1000 species of animals per square meter, including arthropods, nematodes, and protozoa. Soil bacteria and fungi add another 4000-5000 species t o the biodiversity of moist forest soil ecosystems (Heywood 1 9 9 5 ) . Combined, these diverse organisms facilitate the biological degradation of both point and nonpoint sources of soil pollutants. Bioremediation is effective in cleaning up highly polluted soils. For example, an oil gasification plant in southern Ontario produced an oiltar byproduct containing benzene, toluene, xylene, cyanide, heavy metals, polycyclic aromatic hydrocarbons, and phenols that contaminated a n estimated 38,000 m3 of soil (Warith et al. 1992). Application of a nitrogen nutrient and bacterial mixture reduced the various oil-tar pollutants by 40-90% after just 70-90 days of treatment (Warith et al. 1992). The growing interest in bioremediation is due in large measure t o its economic benefits. For example, if bioremediation had been used t o clean up the entire Alaskan shoreline that was contaminated by the Exxon Valdez oil spill in 1989, the cleanup cost would have been less than $0.25 billion rather than the $2.5 billion actual cost (EPA 1995).This tenfold decrease in remediation costs is generally accepted as the standard when

comparing bioremediation with conventional methods such as thermal and physical remediation. The US Geological Survey Toxic Substances Hydrology Program estimates a total cost of $750 billion over the next 30 years to remediate all known hazardous waste sites. This estimate includes S u ~ e r f u n dsites as well as other sites an2 federal facilities (USGS 1995). The use of bioremediation would reduce this cost t o only $75 billion over the same period, a savings of $22.5 billion per year (Table 2). Considering that the United States produces the largest amount of chemical pollution, and assuming a proportion of the total amount that is similar t o the ratio of US markets to world markets for environmental technology, the cost t o remediate chemical pollution worldwide using current technologies is extrapolated t o be $135 billion per year. Using bioremedi-ation, the cost would be approximately $14 billion per year, providing benefits of $121 billion per year (Table 2 ) . Maintaining biodiversity in soils and water is i m ~ e r a t i v eto the continued and improved effectiveness of bioremediation and biotreatment. The presence of large numbers of microorganismal species expands both the variety of and extent to which chemical ~ o l l u t i o nin the environment can be degraded.

Genetic resources increase crop and livestock yields Approximately 250,000 plant species have been described worldwide (Raven and Johnson 1992).Many of these species provide valuable genetic material for some of the most important crop plants for humans. Since 1945, world crop yields have increased between two- and fourfold, depending on the crop. An estimated 20-40% of this increase has been achieved by genetic modification and breeding, which improved hybrid vigor and host plant resistance. Another 30-50% of the yield increase has resulted from increased fossil energy inputs such as commercial fertilizers (Babcock and Foster 1991). Cultural changes, such as doubling the density of crop plants per hectare, are responsible for a n additional 10-50% increase in yield,

depending on the crop. The increases in annual crop yields since 1945 are worth approximately $60 billion per year (USBC 1995). Assuming that the contribution of genetic resources is responsible for 3 0 % of the yield increase, the introduction of new genes a n d genetic modifications through crossing with wild relatives contributes approximately $20 billion per year in increased crop yields t o the United States and an estimated $115 billion per year worldwide (Table 2). Classical plant breeding has increased yields for several crops, such as rice, wheat, and corn, that are important outside the United States. In Asia, for example, the estimated benefits of genetically improved rice and wheat total $1.5 billion per year and $20 billion per year, respectively (Oldfield 1984).A new strain of rice genetically improved through hybridization with other rice genotypes in Asia increased the value of this crop by $ 1 billion within t w o years (Facklam and Facklam 1990). In the United States, the value of improved dwarf rice alone is estimated to have added more than $2.5 billion to the agricultural economy over the last 2 5 years (Raeburn 1995). Genetic resources have also increased production yields in the livestock industry, especially in dairy cattle, hogs, and poultry. For example, milk production per dairy cow was approximately 3600 kglyr in 1935, but the yield is now approximately 8 6 0 0 kglyr (USDA 1995). Similarly, average yearly egg production per hen was only 9 3 eggs in 1930, and it has now risen to 246 eggs (Johnson 1995).Broiler chicken production has also increased dramatically. For instance, in 1930 approximately 1 3 kg of feed was required to produce 1 kg of broiler chicken, whereas only 1.9 kg of feed is needed today (Johnson 1995). These increases in efficiency have resulted from a combination of breeding technology and improved feed and husbandry (Johnson 1995). The total increase in the value of US livestock production is approximately $60 billion per year. Again assuming that one-third of the benefits are due t o genetic breeding, the benefits from the use of biodiversity total at least $20 billion per year BioScience Vol. 47 No. 11

(Table 2); assuming a similar increase for livestock production worldwide, the estimated benefits are $40 billion per year (Table 2 and Figure l ) .

worm. These pests currently cost US farmers $171 million per year in yield losses and insecticide costs (Head 1992). Benedict et al. (1992) predicted that the widespread use of Bt cotton could reduce these costs by Biotechnology as much as 50-90%, saving farmers Advances in biotechnology have en- between $86 and $154 million per abled the transfer of genetic traits year. Widespread pesticide use on both within species and between en- cotton crops would also be greatly tirely different plant and animal spe- reduced. The present economic benefits of cies. Thus, such technologies have the potential to enhance and to accelerate biotechnology products are signifithe genetic modification of both crops cant, conservatively estimated t o be and livestock, improving productiv- between $2 and $3 billion per year in ity, the development of new food the United States (Table 2; Kathuri et al. 1993).Worldwide, current benand fiber crops, and pest control. Biotechnological gene transfer is efits are approximately $6.2 billion currently being used in various fields, per year (Kathuri et al. 1993) and are including agriculture, forestry, vet- projected to increase t o $9 billion erinary and human medicine, phar- per year by the turn of the century maceutical development, energy con- (Table 2; USDC 1984). Nearly half servation, and waste treatment (BIO of the current economic benefits of 1990). Potential environmental and biotechnology relate to agriculture, economic benefits of biotechnology with significant benefits in the pharinclude the reduction of fossil fuel maceutical industry (Kathuri et al. use in agriculture and forestry (i.e., 1993). if crops can be engineered to produce their own nutrients); the reduc- Biological pest control tion of artificial inputs, such as fertilizer and insecticides (i.e., if crops Approximately 70,000 pest species can be engineered to fix their own attack agricultural crops throughnitrogen and produce their own in- out the world (Pimentel 1991a). Besecticidal compounds); and more tween 3 0 % and 8 0 % of the pests in cost-effective and environmentally any geographic region are native spefriendly waste management practices, cies. Thus, indigenous insects and such as bioremediation (i.e., if plants pathogens have moved from feeding or microbes can be engineered t o be on native vegetation t o becoming pests on introduced crops (Hokkanen better bioremediators). For example, by using biotechno- and Pimentel 1989). Approximately 9 9 % of pests are logical approaches t o transfer genes that allow legumes to form symbio- controlled by natural enemy species ses with nitrogen-fixing bacteria into and host plant resistance (DeBach nonlegume crops, such as wheat and and Rosen 1991). Each insect pest corn, these crops may gain the abil- has an average of 10-15 natural enity to form these symbioses. Such a n emies that help to control it (van den advance would significantly reduce Bosch and Messenger 1973). Howthe need for commercial nitrate fer- ever, some pests, such as the gypsy tilizers (Mannion 1995). However, moth (Lymantria dispar), have as because the molecular mechanisms many as 100 natural enemies (Pimenthat are required for symbiotic ni- tel 1988). However, the value of these natural enemies to pest control trogen fixation are complex-involvis often overlooked. ing at least 1 7 genes in the plantDespite heavy pesticide applicaachieving this goal may require an investment in research over several tion (0.5 x l o 6 tlyr) at an estimated cost of $ 6 billion, plus various decades. Biotechnology approaches have nonchemical controls, including been used successfully t o incorpo- natural enemies, US crop losses to rate a toxin gene from Bacillus pests are estimated t o reach 3 7 % per thuringiensis (Bt) into cotton plants year (Pimentel et al. 1991). This loss to control caterpillar pests, includ- is equivalent t o an estimated $50 ing the cotton bollworm and bud- billion per year loss in food and fiber December 1997

in the United States, despite all efforts t o control these pests. O n the positive side, pesticide applications reduce potential US crop losses by approximately $20 billion per year, natural enemies reduce losses by approximately $12 billion per year (Table 2), and host plant resistance and other nonchemical pest controls reduce losses by a n additional estimated $8 billion per year (Pimentel 1997). Thus, pest control benefits total at least $40 billion per year. Without pesticides, natural enemies, host plant resistance, and other nonchemical controls, 6 7 % of crops would be lost, at a cost of approximately $90 billion per year (Pimentel 1997). Worldwide, pests reduce the yields of major crops by approximately 4 2 % each year, despite the application of an estimated 2.5 x l o 6tlyr of pesticides at a cost of $26 billion, plus the benefits of various nonchemical controls (Oerke et al. 1994). The total cost of losses to pests is estimated to be $244 billion per year. Without pesticides, natural enemies, host plant resistance, and other nonchemical controls, 7 0 % of crops could be lost t o pests (Oerke et al. 1994), increasing the cost of losses t o approximately $400 billion per year (Oerke et al. 1994). We estimate from field experience that natural enemies provide 6 0 % of the benefits from nonchemical controls. Therefore, natural enemies provide approximately $100 billion worth of pest control worldwide per year (Table 2 and Figure 1). Natural enemy species also are effective in protecting forests from pests. For example, bird predation on insects is estimated t o provide annual benefits in insect control equivalent t o as much as $180/ha in US spruce forests (Diamond 1987). All together, birds and all other natural enemies provide estimated annual benefits t o forests of $18/ha. Thus, a conservative estimate of the benefits provided by all natural enemies to US forests on approximately 270 million hectares is approximately $5 billion per year. Extrapolating to world forests, which cover 1 4 times the area of US forests, the value of the protection to forests offered by natural enemies is estimated to be $60 billion per year worldwide (Table 2). 75 1

The d e v e l o ~ m e n tof ~ e r e n n i a l proximately $3/ha by preventing insect and disease damage in forests grain crops could also reduce fuel (Pimentel 1988). Overall, the value consumption, by as much as 7 2 % Host plant resistance, including char- of host plant resistance to forests is per hectare (Wagoner et al. 1993).If acteristics such as hairs, hardness, approximately $800 million per year US corn were grown as a perennial, - savings in diesel fuel alone could nutrient changes, toxins, and repel- in the United States and a ~ ~ r o x i the lents, is another major control method mately $ 1 1 billion per yearLworld- reach $300 million per year because the energy expended for sowing and for insect and plant pathogen pests. wide (Table 2 and Figure 1 ) . Pests freauentlv evolve tolerance frequent cultivation would be elimiUsing resistant crop varieties in agriculture is economically and environ- to the resistance factors incrops (e.g., nated (Raeburn 1995). Estimates of the economic benmentally beneficial because such va- oat lines previously resistant t o oat efits of perennial grain development rieties sienificantlv reduce the need rust disease become susce~tible t o u

for pesticides. For example, resis- it). T o overcome such tolerance, ad- can be based on potential reductions tance genes have now been identified ditional genetic diversity is needed. in soil erosion, fossil fuel use, and for all major cereal grain pathogens, Genes from wild and cultivated plant environmental pollution. Planting pereducing the need for the application species that are regularly exposid t o rennial grains could save approxiof pesticides on these crops. endemic diseases and, thus, main- mately $20 billion per year in reIn the wild, all plant species ex- tain new forms of resistance can then duced soil erosion (Pimentel et al. hibit some degree of natural host be transferred t o croDs bv both tradi- 1995) and $9 billion per year in u

plant resistance, which protects them tional breeding and' bibtechnology reduced tractor fuel inputs (Wagoner et al. 1993). In addition, there from many of their pests (Subra- (Harlan 1977). would be savings of at least $ 1 bilmanian 1977).For instance, Hanover lion per year in reduced agricultural (1975) reported that there may be Perennial cereal grains and environmental pollution because approximately 1000 chemicals in a single tree, yielding a multitude of The dominant grain crops grown pesticide and fertilizer use would be ~ o t e n t i a lcombinations to ~ r o v i d e worldwide are rice, wheat, corn, reduced (Pimentel and Greiner 1997). for vest control. Through advances millet, barley, and rye. In temperate The potAtial economic benefits a;in i l a n t breeding and-biotechnol- zones, most grain crops are planted sociated with the development and ogy, such resistance genes are fairly as annuals because they are not cold use of perennial grains in the United quickly and easily transferred from tolerant. Annual cropping is also used States could therefore total as much wild t o cultivated crops to improve in the tropics as a way t o deal with as $17 billion per year (Table 2);worldcrop resistance. weeds, insects, and plant pathogens wide, a perennial grain system could From 75% to 1 0 0 % of agricul- (Pimentel 1991b). Clearing wild veg- be worth as much as $170 billion per tural crops contain some degree of etation by tillage eliminates many pest year (Table 2 and Figure 1). Although none of the major grain host plant resistance (Oldfield 1984, insects, plant pathogens, and weeds Pimentel et al. 1989). These resis- before planting an annual crop. crops that are grown now are perenCereal grains are produced on nials worldwide, some verennial tance traits improve yields and, thus, economic returns t o growers. For 7 0 % of arable land worldwide; pro- grain types have been identified in example, when host plant resistance duction totals approximately 2 x l o 9 the wild. For example, a perennial was integrated into a control pro- t/yr (USDA 1995). These grains pro- corn species that is highly restricted gram for potatoes, only half the nor- vide 8 0 % of the food that humans in range and is infertile with cultimal amount of fungicide was needed consume. Planting large areas to an- vated corn was discovered in the to suppress early and late blights on nual crops damages the immediate Sierra de Manantlan Mountains in potatoes (Shtienberg et al. 1994), a agroecosystem and beyond. For in- central Mexico approximately 20 potential savings of approximately stance, the practice of spring and fall y e a r s a g o ( P r e s c o t t - A l l e n a n d $ 7 million per year in the United States tilling leaves the soil exposed and Prescott-Allen 1986). It is possible (Pimentel et al. 1991). We estimate makes it susceptible to water and wind that this perennial corn genotype or that in the United States. the Dres- erosion (Pimentel et al. 1995). In fact. another one that has been identified ence of host plant resistance pre- US agridultural practices are respon: in South America might provide the vents 4 0 % of the $20 billion in po- sible for 64% of the total pollution basis for the eventual development tential losses t o pest insects and that is entering streams and 5 7 % of of a perennial corn genotype. Achievpathogens, amounting to a savings of the pollutants that are entering lakes ing a commercial perennial corn, however, will be extremely difficult $8 billion per year; worldwide savings through erosion (Miller 1992). In contrast t o annual grains, pe- (Raeburn 1995).Perennial wheat and are estimated to be approximately rennial grains can be grown and har- sorghum genotypes exist that could $80 billion per year (Table 2). Similarly, host plant resistance vested continuously for a period of be the basis of perennial cropping of helps t o control damage from insect 4-5 years without tilling and replant- these grains as well (Wagoner 1990). pests and plant pathogens in forests. ing (Piper 1993). Soil erosion could Host plant resistance is about as ef- be reduced by as much as 5 0 % be- Pollination fective as natural enemies (Pimentel cause soils are left relativelv undis1991a), so we estimate that each turbed and covered with veietation Pollinators, such as bees, butterflies, birds, and bats, provide substantial year, host plant resistance saves ap- (Moffat 1996).

Host plant resistance and pest control

752


benefits to the maintenance. diversity, and productivity of both agricultural and natural ecosystems (Buchmann and Nabhan 1996). As much as one-third of the world's food production relies either directly or indirectly on insect pollination (Richards 1993). Although many major crops are self- or wind pollinated, others require and benefit from insect pollination to increase quality or increase yields (Richards 1993). Even some self-pollinated domesticated crops, such as the banana, rely on animal-pollinated wild relatives to provide the genetic diversity that is essential for crop improvement (Fujita and Tuttle 1991). Pollinator diversity depends on ecosystems that are rich in diverse vegetation (LaSalleand Gould 1993). Approximately 6000 species of native plants, or approximately onethird of the total species in the United States, are outcrossed via pollinat o r ~ An . ~ estimated one-third of the world's plant species (Holsinger 1992) depend on biological cross-pollination. In US agriculture, approximately 130 crop species are insect pollinated (Southwick 1992). Insects are the largest group of pollinators, with honeybees estimated to provide approximately 80% of all insect pollination (Robinson et al. 1989). In North America, approximately 4000 bee species have some ability to pollinate (Robinson et al. 1989, Southwick 1992).Worldwide, at least 20,000 species of bee pollinators have been described (O'Toole and Raw 1991). Although most estimates of the economic value of pollination in agricultural systems focus on honeybees, honeybees frequently receive credit for pollination that is carried out by other bee species or other insects (Richards 1993). The value of pollination to US agricultural production is estimated to be $40 billion per year when the value of insectpollinated legumes fed to cattle is included (Robinson et al. 1989). Assuming conservatively that the economic value of animal pollinators worldwide is at least five times that in the United States, the contribution of animal pollination t o world agriculture is estimated t o 5 e e footnote 1.

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be $200 billion per year (Table 2 and Figure 1). Pollinator biodiversitv is also an advantage in natural ecosystems, whose diversity of vegetation and habitat often requires pollinator species with varied characteristics (LaSalle and Gould 1993). For example, different flower sizes and shapes necessitate types of pollinators suited to the needs of particular flowers (Neff and Simpson 1993). Habitat fragmentation and loss " are causing precipitous declines in wild pollinators, thereby threatening their beneficial activities in both natural and agricultural systems. Specifically, habitat degradation adversely affects pollinator food sources, nesting sites, and mating sites. Diseases and pesticides also decimate pollination systems. In the United States, populations of wild bees are decreasing in agricultural regions (Richards 1993). In California, for instance, significant habitat alterations combined with vesticide use have led to the reductio; of most wild bees, forcing farmers to rely on rented honeybee colonies for pollination."

ecotourism is the second largest industry in Costa Rica, where it generates $500 million per year (Podgett and Begley 1996). Munasinghe and McNeely ( 1 9 9 4 ) estimate t h a t ecotourism contributes between $0.5 and $1 trillion per year to the world economy (Table 2 and Figure 1).

Harvest of food and pharmaceuticals from the wild

In the United States, commercial and sport fisheries represent the largest proportion of the harvested wild biota, with 5.5 million tons harvested each year at a value of $2.5 billion (Table 2; USBC 1995). Worldwide, the estimated 95 million tons of seafood harvested each year is valued at approximately $82 billion (Thorpe et al. 1995). This figure does not include the contributions of commercially produced aquaculture and algal products (Table 2; Radmer 1996). Overall, fish provide less than 1% of the world's food (and less than 5% of protein; FA0 1991). The 6 million tons of food products harvested annually from terrestrial wild biota in the United States include large and small animals such as deer and squirrels and products Wild animals and ecotourism such as maple syrup, nuts, blueberSport fishing, hunting, and associ- ries, and algae. Harvested wild blueated recreational pursuits generate berries are valued at $25 million per millions of dollars each year world- year (Harker 1995), and the 6 milwide. For instance, the US public lion liters of US maple syrup prospends approximately $29 billion per duced each year (USDA 1995) are year on fishing (Coull1993) and $12 valued at $57 million. In total, wild billion per year on hunting (USBC foods including seafood contribute an 1995). Thus, $41 billion per year is estimated $3 billion per year to the a conservative estimate of the eco- US economy (Table 2; USBC 1995). A world value for foods harvested nomic value of wild animals to the US economy (Table 2). Estimated from the wild cannot be extrapoworldwide expenditures for hunting lated from US values because people and for fishing total approximately in developing countries depend more extensively on wild biota for their $85 billion per year (Table 2 ) . The growing ecotourism industry food than Americans. A reasonable generates an enormous amount of estimate is that $90 billion per year money for economies around the in food and in related products are world. Nonconsumptive recreation, harvested from forests and used by such as birdwatching, in the United approximately 300 million people in States contributes approximately $18 developing countries (Pimentel billion per year (Table 2; USDI 1991). 1997a).This harvested food is suffiEcotourism is fast becoming an espe- cient to provide from 5 % to 10% of cially lucrative industry for some the food that is consumed by people developing nations. For example, living in these forested areas. An equal amount of food, worth ap'E. C. Mussen, 1996, personal communica- proximately $90 billion per year (Pimentel et al. 1997a), is harvested tion. Department of Entomology, University of California, Davis, CA. from nonforested terrestrial areas in 753

the world, bringing the total to approximately $180 billion per year in food and related products that are harvested from natural terrestrial ecosystems (Table 2 and Figure 1). In the United States, pulp and timber products generate approximately $8 billion per year (USBC 1995), whereas the worldwide return is estimated to be $84 billion per year (Table 2; Groombridge 1992). In addition to food and wood products, plants with medicinal properties are harvested from the wild. Indeed, nearly half of the medicinal prescriptions that are now in use originated from a wild plant (Plotkin 1991), and between 35,000 and 70,000 species of plants are used directly as medicines (Farnsworth and Soejarto 1991). For instance, derivatives from 2500 plant species have been approved as medicines in India alone (Principe 1991). Plant-based drugs and medicines in the United States have a market value of $36 billion per year (USBC 1995), and those on the Asian market have a value of $70.5 billion per year (Gerry 1995). Thus, we estimate that the economic return in the world market of plant-based drugs is worth more than $200 billion per year. Of this estimate, over-thecounter plant-based drugs have an estimated market value of $20 billion per year in the United States and $84 billion per year worldwide (Table 2; Pearce and Moran 1994).

Forests sequestering carbon dioxide Trees, like all growing vegetation, seauester carbon dioxide and therebv help to reduce global warming. Rising temperatures and changing global rainfall patterns are likely to alter crop production. Global warming is also projected to melt some of the ice caps, which could cause the world sea level to rise. resulting" in serious coastal flooding and damage to vast coastal regions. Pearce (1991) estimates that a diverse tropical fo>est sequesters 10 t ha-' yr-' of carbon. Based on his "damage avoided" approach, the net reduction of carbon by forests is worth $20 per ton of carbon dioxide removed in terms of reducing the coastal damage that would Fesult 754

from the sea level rise associated with global warming (Fankhauser 1993). Thus, for the 1.8 billion hectares of tropical forests (WRI 1994), approximately 2.5 tlha of net carbon is sequestered each year, with an associated damage-avoided value of approximately $90 billion per year. Pearce (1991)estimates that the 1.5 t . ha-' yr-I of carbon sequestered in the 1.5 billion hectares of world temperate forest has a total value of $45 billion per year. The world total in damage avoided is thus $135 billion per year (Table 2 and Figure 1).For the 210 million hectares of US forests, we calculate a total value of $6 billion per year in damage avoided (Table 2). These estimates should be considered conservative because they are based on projected coastal damage from sea level rise and do not include the many other detrimental environmental effects of global warming on food crop production and on human health (WRI 1994).

Costs of conserving biodiversity

Increased biomass has numerous benefits in crop, pasture, and forest production. It reduces soil erosion, diseases. and r a ~ i dwater runoff: improves recycling of soil nutrients and pest biocontrol; increases water percolation into the soil; and provides other economic benefits. Conserving water resources and biodiversity saves money. Agriculture consumes approximately 80% of the total water per year in the United States annually. Conserving water in agriculture would be profitable for taxpayers and would increase water availability for biodiversity. Currently, approximately $4.4 billion in public funds is used to subsidize water for western agriculture, and much of the water comes from the Colorado River (Pimentel et al. 1997b). Eliminating., this enormous subsidy would conserve water, improve biodiversity in the overdrafted Colorado River. and save taxpayers billions of dollars.

Conclusions The estimated economic and environmental benefits from all biota (biodiversity), including their genes, are substantial. For the United States, their services contribute an estimated $319 billion per year. Relative to the $6 trillion per year of US gross domestic product (GDP), the services amount to 5 % of GDP (USBC 1995). For the world, the benefits are estimated to be $2928 billion per year, or approximately 1 1 % of the total world economy of $26 trillion per year.6 These estimated benefits are clearly conservative. For example, another similar study estimates world economic benefits of biodiversity to be $33,000 billion per year (Costanza et al. 1997). Our study endeavored to increase the understanding of the many essential services that diverse species provide to humans. These services include organic waste disposal, soil formation, biological nitrogen fixation, crop and livestock genetics, biological control of pests, plant pollination, drugs and medicines, and the vast genetic resources that will be required for future sustainability of the environment and human society.

Some aspects of conserving biodiversity are expensive, although they may return important dividends. For example, as of 1993, $20 million had been spent on research and conservation to save the California condor (Cohn 1993), and the cost of possible measures to protect salmon in the Snake and Columbia rivers has been estimated at between $2 and $211 million (GAO 1993). Moreover, the costs of rearing even a nonendangered bird species such as those that are typically killed in oil spills can be highly expensive. For instance, the cost of replacing a bird that was killed by the Exxon Valdez oil spill was an average of $800 per bird. Obviously, this type of conservation of biodiversity is extremely costly. Other types of resource conservation not only protect biodiversity but also provide significant economic dividends at the same time. For example, biomass conservation aids in increasing species because all organisms, except for plants, which produce their own protoplasm, depend on the biomass from plants for energy and other nutrients. Thus, more biomass generally means that there are 6N. Myers, 1996, personal communication. more species (Pimentel et al. 1992). Oxford University, Oxford, UK.


The current rate of s ~ e c i e extincs tion is now approximately from 1000 to 10,000 times higher than natural extinction rates and is reducing biodiversity. Growing human populations and their associated increase in activities are destroying natural and other habitats that are required for the survival of many plant and animal species. Some threats to agriculture, forestry, and natural ecosystems are related to the losses of pollinators, natural enemies of pests, and fishes. Pollution of ecosystems and the depletion of basic resources have reached dangerous levels. If future generations are to live in a safe, productive, and healthy environment, sound policies and effective conservation programs must be implemented t o protect biodiversity (Pimentel et al. 1992) before it is too late for meaningful action.

Acknowledgments We thank the following people for reading an earlier draft of this article, for their many helpful suggestions, and, in some cases, for providing additional information: C. C. Delwiche, Professor Emeritus, University of Oregon, Corvallis, OR; Johanna Dobereiner, Centro Nacional de Pesquisa em Agrobiologia, Rio de Janeiro, Brazil; Jiirg Huber, Federal Biological Research Centre, Darmstadt, Germany; Stephen R. Kellert, Yale University, New Haven, CT; Lori Lach, Tellus Institute, Boston, MA; John LaSalle, International Institute of Entomology, London; A. R. Main, University of Western Australia, Nedlands, Perth, Western Australia; Eric C. Mussen, University of C a l i f o r n i a , Davis, CA; Norman Myers, Oxford University, Oxford; Ida N. Oka, Bogor Research Institute for Food Crops, Bogor, Indonesia; M a u r i z i o G. Paoletti, Universita' Degli Studi di Padova, Padova, Italy; David Pearce, Center for Social and Economic Research on the Global Environment, University College, London; Charles Perrings, University of York, Heslington, York, UK; Jon K. Piper, The Land Institute, Salina, Kansas; Jorge Rabinovich, Universidad de Belgrano, Buenos Aires, Argentina; Peter H . Raven, Missouri Botanical Garden, St. Louis, MO; Walt Reid, World Resources

December 1997

Institute, Washington, DC; Gene Robinson, University of Illinois, Urbana, IL; Bernhard Schmid and Irmi Seidl, University of Zurich, Zurich, Switzerland; Hope Shand, Rural Advancement Foundation International, Pittsboro, NC; V. Kerry Smith, Duke University, Durham, NC; David Takacs, California State University, Seaside, CA; Laura Westra, University of Windsor, Windsor, Ontario, Canada; Ingrid H . Williams, IACRRothamsted, Harpenden, Hertfordshire, UK; and Richard Cahoon, Celia Harvey, William Lesser, and Marcia H . Pimentel a t Cornell University, Ithaca, NY.

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References cited Measuring the Potential Contribution of Plant Breeding to Crop Yields: Flue-Cured Tobacco, 1954-87 Bruce A. Babcock; William E. Foster American Journal of Agricultural Economics, Vol. 73, No. 3. (Aug., 1991), pp. 850-859. Stable URL: http://links.jstor.org/sici?sici=0002-9092%28199108%2973%3A3%3C850%3AMTPCOP%3E2.0.CO%3B2-S

The Flight of the California Condor Jeffrey P. Cohn BioScience, Vol. 43, No. 4. (Apr., 1993), pp. 206-209. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199304%2943%3A4%3C206%3ATFOTCC%3E2.0.CO%3B2-N

Flying Foxes (Chiroptera: Pteropodidae): Threatened Animals of Key Ecological and Economic Importance Marty S. Fujita; Merlin D. Tuttle Conservation Biology, Vol. 5, No. 4. (Dec., 1991), pp. 455-463. Stable URL: http://links.jstor.org/sici?sici=0888-8892%28199112%295%3A4%3C455%3AFF%28PTA%3E2.0.CO%3B2-6



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Benefits and Risks of Genetic Engineering in Agriculture D. Pimentel; M. S. Hunter; J. A. LaGro; R. A. Efroymson; J. C. Landers; F. T. Mervis; C. A. McCarthy; A. E. Boyd BioScience, Vol. 39, No. 9. (Oct., 1989), pp. 606-614. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28198910%2939%3A9%3C606%3ABAROGE%3E2.0.CO%3B2-3

Conserving Biological Diversity in Agricultural/Forestry Systems David Pimentel; Ulrich Stachow; David A. Takacs; Hans W. Brubaker; Amy R. Dumas; John J. Meaney; John A. S. O'Neil; Douglas E. Onsi; David B. Corzilius BioScience, Vol. 42, No. 5. (May, 1992), pp. 354-362. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199205%2942%3A5%3C354%3ACBDIAS%3E2.0.CO%3B2-%23

Environmental and Economic Costs of Soil Erosion and Conservation Benefits David Pimentel; C. Harvey; P. Resosudarmo; K. Sinclair; D. Kurz; M. McNair; S. Crist; L. Shpritz; L. Fitton; R. Saffouri; R. Blair Science, New Series, Vol. 267, No. 5201. (Feb. 24, 1995), pp. 1117-1123. Stable URL: http://links.jstor.org/sici?sici=0036-8075%2819950224%293%3A267%3A5201%3C1117%3AEAECOS%3E2.0.CO%3B2-4

Water Resources: Agriculture, the Environment, and Society David Pimentel; James Houser; Erika Preiss; Omar White; Hope Fang; Leslie Mesnick; Troy Barsky; Stephanie Tariche; Jerrod Schreck; Sharon Alpert BioScience, Vol. 47, No. 2. (Feb., 1997), pp. 97-106. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199702%2947%3A2%3C97%3AWRATEA%3E2.0.CO%3B2-D



The Future of Biodiversity Stuart L. Pimm; Gareth J. Russell; John L. Gittleman; Thomas M. Brooks Science, New Series, Vol. 269, No. 5222. (Jul. 21, 1995), pp. 347-350. Stable URL: http://links.jstor.org/sici?sici=0036-8075%2819950721%293%3A269%3A5222%3C347%3ATFOB%3E2.0.CO%3B2-N

Algal Diversity and Commercial Algal Products Richard J. Radmer BioScience, Vol. 46, No. 4, Marine Biotechnology. (Apr., 1996), pp. 263-270. Stable URL: http://links.jstor.org/sici?sici=0006-3568%28199604%2946%3A4%3C263%3AADACAP%3E2.0.CO%3B2-C